It is unnerving enough to walk around a trade fair and see your own face projected on a giant screen.

It can detect faces in motion, faces at a distance and faces among other faces

Frances Zelazny, Visionics

But it is even more unnerving when a computer instantly spots your face on the picture, circles it in yellow and checks it in seconds against a database of known troublemakers.

I was caught on camera by Visionics Corporation's face recognition system, which is already installed at Reykjavik Airport in Iceland.

It is part of a whole exhibition hall full of security products on display at the giant CeBIT 2002 technology fair in Hanover, Germany.

Beards no problem

"It can detect faces in motion, faces at a distance and faces among other faces," Visionics' Frances Zelazny told BBC News Online.

The system looks at bone structure

The system works by looking at the bone structure of people's faces, thereby avoiding problems caused by facial hair and spectacles.

"There are about 80 points associated with bone structure on the face and we need only 14 to 22 to make a match," Ms Zelezny said.

The basic system costs between $35,000 and $50,000, but can be scaled up to cope with busier places and larger numbers of faces.

Mugshot top 10

Security staff feed the system with pictures of people they view as a threat. Even poor quality pictures from old documents or security cameras are enough to go on.

The finger makes light work of passwords

Then, when the system is running at an airport or a border crossing, every time it sees a face, it throws up a list of the best 10 matches it has for that face.

Even if only one of those 10 pictures is a person from the danger list, the system alerts security staff to carry out a full identity check.

For less high-profile locations, the German electronics company Siemens has produced a fingerprint mouse called the ID mouse.

Instead of entering a password or a personal identification number (Pin), computer users can place their finger on a pad in the middle of their computer mouse to log themselves into their system or gain access to protected files.

Dead man's finger

Siemens sees a market in the United States, where legislation now requires strict protection for computers holding patient data in hospitals and clinics.

"People tend to pick their partner's names as passwords or just write them down," said Siemens' Joerg Dahmen von Buchholz-Daburger. "Our system means they can just use their fingerprint instead."

The mouse and the software needed to log on and off sell for about £75.

Its accuracy rate was good enough for it to be used for home banking, Mr Dahmen von Buchholz-Daburger said.

The mouse software was even intelligent enough to spot the difference between a live finger and a dead finger, or even the finger of a person who had spent too long in the bath, he added.